1. Field of the Invention
This invention relates to a television receiver and in particular to a television receiver that can receive television broadcast signals in response to two different television broadcast forms.
2. Description of the Related Art
Hitherto, as an example of this kind of television receiver, a television receiver that can selectively receive either of TV (television wave) broadcasting and CATV (cable television) broadcasting has been known. Since they differ in assigned channel frequencies, if which television broadcasting is to be received is not previously known, the channel frequencies are not known either, thus the user needs to set a predetermined changeover switch in response to the television broadcasting to be received.
However, setting a changeover switch as mentioned above is burdensome for the user and television broadcasting cannot normally be received in some cases because of erroneous setting. Thus, various configurations for a television receiver to determine which television broadcasting can be received and for executing internal setting based on the determination result have been developed.
As an example, Japanese Patent Unexamined Publication No. Hei. 6-326935 discloses the following configuration: Attention is focused on the fact that CATV broadcasting channels are assigned to a specific frequency band to which TV broadcasting channels are not assigned, and a presearch is made for a CATV broadcasting channel on the specific frequency band, whereby which of CATV broadcasting and TV broadcasting can be received is determined. Channel presetting is executed in response to the determination result and channel selection control is performed based on the channel presetting contents.
The conventional television receiver described above involves the following problem:
Surely, setting a changeover switch is not necessary for user""s convenience and a case in which television broadcasting cannot normally be received because of erroneous setting cannot occur. However, after a presearch is made for a CATV broadcasting channel on the specific frequency band, channel presetting is newly executed, thus it takes time in the channel presetting in some cases.
It is therefore an object of the invention to provide a television receiver that can decrease the time required for channel presetting while determining which television broadcast form can be received if television broadcast signals can be received in response to two television broadcast forms.
To achieve the above object, according to the invention, there is provided a television receiver comprising: signal reception means for receiving and outputting a signal of any desired frequency in response to a first television broadcast form in which predetermined channel frequencies are assigned and a second television broadcast form in which channel frequencies are assigned to a specific frequency band not assigned in the first television broadcast form although the same channel frequencies as or channel frequencies close to the channel frequencies assigned to the first television broadcast form are assigned; reception instruction means for instructing the signal reception means to receive a signal of each channel frequency in response to the second television broadcast form; station existence determination means for roughly continuously changing the reception frequency of the signal reception means on a frequency band containing the channel frequencies in the first television broadcast form close to each channel frequency specified by the reception instruction means and determining whether or not a station exists based on the output; channel memory means having as many memory positions as the number of channels in the second television broadcast form for storing the determination result of the station existence determination means in the corresponding memory position; television broadcast form determination means for determining which of a signal in the first television broadcast form and a signal in the second television broadcast form can be received based on the determination result of the station existence determination means as to each channel within the specific frequency band assigned only to the second television broadcast form after completion of storage processing for all memory positions in the channel memory means; and reception control means, to cause the signal reception means to receive a station-existing channel based on the storage contents of the channel memory means, if the television broadcast form determination means determines that a signal in the first television broadcast form can be received, the reception control means matching the station-existing channel with the channel in the first television broadcast form and causing the signal reception means to receive the channel.
In the television receiver configured above, a signal of either of the first television broadcast form in which predetermined channel frequencies are assigned and the second television broadcast form in which channel frequencies are assigned to a specific frequency band not assigned in the first television broadcast form although the same channel frequencies as or channel frequencies close to the channel frequencies assigned to the first television broadcast form are assigned can be received. At the initial introduction time, etc., channel presetting is executed before the television receiver is used. In the channel presetting, if the reception instruction means instructs the signal reception means to receive a signal of each channel frequency in response to the second television broadcast form, the signal reception means receives the signals of the channel frequencies in sequence based on the instruction. At this time, the station existence determination means roughly continuously changes the reception frequency of the signal reception means on a frequency band containing the channel frequencies in the first television broadcast form close to each channel frequency and determines whether or not a station exists based on the output. On the other hand, the channel memory means has as many memory positions as the number of channels in the second television broadcast form for storing the determination result of the station existence determination means in the corresponding memory position.
Upon completion of storage processing for all memory positions in the second television broadcast form in the channel memory means, the television broadcast form determination means determines which of a signal in the first television broadcast form and a signal in the second television broadcast form can be received based on the determination result of the station existence determination means as to each channel within the specific frequency band assigned only to the second television broadcast form. The reception control means causes the signal reception means to receive a station-existing channel based on the storage contents of the channel memory means. At this time, if the television broadcast form determination means determines that a signal in the first television broadcast form can be received, the reception control means matches the station-existing channel with the channel in the first television broadcast form and causes the signal reception means to receive the channel.
That is, the station existence determination means determines whether or not a station exists based on the channel frequency in the second television broadcast form; it determines whether or not a station exists on the frequency band containing the channel frequencies in the first television broadcast form close to each channel frequency in the second television broadcast form. Therefore, if the signals only in the first television broadcast form can be received, a station-existing channel frequency is detected. However, since the memory position in which the station-existing channel is stored is predicated on the second television broadcast form, no memory position consistency may occur between the first and second television broadcast forms. Then, the reception control means matches the station-existing channel with the channel in the first television broadcast form and causes the signal reception means to receive the channel.